In producing magnetic recording media, there is a recurring need to transport large quantities of recording tape from the point of tape manufacture to other locations for final loading into cassettes, cartridges, or other carriers. It is common to transport the tape in the form of relatively large rolls, called pancakes. A pancake of 1.27 cm (0.5 in) wide tape is typically wound on a hollow annular core having an outer diameter of 11.4 cm (4.5 in), and a width of 1.8 cm (0.7 in), slightly larger than the width of the tape. The outer diameter of the pancakes is typically about 35.6-40.7 cm (14-16 in). Shipping these tape pancakes over long distances under conditions of mechanical shock and vibration requires that they be well supported.
One primary form of damage to pancakes is axial shifting of the layers of tape relative to the pancake such that the pancake is no longer flat. This shifting, called core drop, hub drop, popped strands, or tape shift, can be caused by a stack of pancakes being dropped on a hard floor or being transported over rough or bumpy surfaces. Other problems and damage caused with known pancake containers include the offsetting of a portion of the pancake, called "upset," rotation of the core relative to the pancake, and transfer of cushion adhesive to the tape.
While effective protection of the tape in the pancake stacks is essential, the magnetic tape market is very price-competitive. Thus, protective packaging must be low cost, both in the packaging material itself, and in the labor required to apply and remove the packaging. It is also desirable to minimize the amount of packaging waste material which is discarded.
Known methods of protecting pancakes during shipping generally involve sliding several pancakes over a shaft or hollow tube, placing resilient spacers between each pancake, and placing a solid end plate on the top and bottom of the stack. The stack can be held together by shrink wrap film, as disclosed in U.S. Pat. No. 4,955,471.
U.S. Pat. No. 4,883,178 eliminates shrink wrap and discloses holding a pancake stack together with a threaded member running coaxially along the center of the stack, and a nut which tightens on an end plate. The compression is created by the threaded member being disposed within the pancake cores.
U.S. Pat. No. 4,708,246 discloses spacers and other packaging features which improve compression control. However, sometimes spacers move during shipping and can generate debris. Also, some spacer materials can create static which attracts debris to the pancakes.
Radially expanding mandrels are also known. U.S. Pat. No. 4,124,173 discloses an inflatable tube inside of an expandable mandrel. Cam mechanisms which press cylinder segments outwardly when a central shaft rotates relative to the outer segments are also known. U.S. Pat. No. 4,516,786 discloses a rotatable core chuck and U.S. Pat. No. 4,730,779 discloses an expanding assembly for a web-coiling core.
U.S. Pat. No. 5,094,346 assigned to Minnesota Mining and Manufacturing Company stacks pancakes on a mandrel within a container. The mandrel could radially expand to secure the pancakes and/or the pancakes could be secured by axial pressure.